In brachytherapy, and especially in in-vivo brachytherapy, a radiation source is placed within the body at a position within or next to a tissue requiring radiation treatment. Several forms of cancer, such as prostate cancer, are treated with brachytherapy. In these forms of treatment it is important that the radiation source is placed at a predetermined position within the corpus to obtain the most effective treatment of the cancerous tissue. If the radiation source is not placed at the correct position, the tissues could potentially receive wrong radiation doses leading to under-dosing and/or overdosing affecting the efficacy of the treatment.
In an example, the energy emitting sources may be a radioactive source. Some of the sources emit a relatively low amount of energy (in the so-termed low-dose rate brachytherapy) and are placed permanently within the body by means of, for example, a needle. Some of the energy emitting sources emit a relatively large amount of energy (in the so-termed high-dose rate brachytherapy) and are temporarily placed at a specific position next to the tissue to be treated in, for example, a catheter. In high-dose rate brachytherapy the radiation source is, for example, coupled to a wire and the radiation source is fired into the catheter to a predefined position which relates to the length of the wire. Research has shown that in these embodiments of high-dose rate brachytherapy the radiation source does not always reach the predefined position. There is a need for an independent check of the position of the radiation source within the catheter.
Also in other forms of therapy an energy emitting source is guided through a probe, needle or, for example, a catheter into the corpus. In these forms of therapy it is also required to know the exact position of an energy emitting source within the body. An example of such therapeutic technique is laser induced thermal therapy wherein an optical fiber is inserted through a probe into a tumor and laser light is guided to the tip of the optical fiber. In laser induced thermal therapy it is not only important to know whether the optical fiber reached the tip of the probe and where the probe-tip actually is, but it is also important to know how much the optical fiber protrudes out of the probe. Thus, it is required to have an independent check to determine the relative position of the optical fiber with respect to the probe.
Published patent application U.S. Pat. No. 6,447,438 relates to an apparatus and method for locating therapeutic seeds implanted in the human body. The disclosure relates to low-dose rate brachytherapy for treating prostate cancer. In such a therapy, energy emitting therapeutic seeds are implanted in the prostate via needle. Prior to the treatment a treatment plan is made which prescribes the position of the treatment seeds within the prostrate. In practice it is relatively difficult to be sure about the position where the therapeutic seeds are implanted in the prostate and the efficacy of the treatment decreases if the seeds are implanted at another position than the prescribed position. The cited patent application provides an apparatus and a method which may be used to locate already implanted therapeutic seeds. This information may be used, during the process of implanting the therapeutic seeds, to update the treatment plan. According to the provided reference, the therapeutic seeds are partially ferromagnetic and are caused to vibrate by a magnetic field and the vibrating therapeutic seeds are identified by reflections of ultrasonic signals transmitted to the therapeutic seeds. The information provided by the apparatus and the method of the cited reference relates to already implanted therapeutic seeds and does not relate to a position of a seed just before the actual moment of implantation. Thus, the apparatus and the method may be useful in the context of updating the treatment plan, but do not help a surgeon in implanting the seeds at the predefined positions.